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Heartworm preventive resistance and Immiticide shortage

Concern has been ongoing about possible heartworm resistance to macrocyclic lactone preventives. The Companion Animal Parasite Council (CAPC) and the American Heartworm Society (AHS) created a joint statement regarding heartworm resistance, prevention, testing, and treatment, and the key recommendations for veterinarians are presented here. To see a text-only version of this article, click here.

• Keep in mind that, when used properly, macrocyclic lactones remain effective as a prophylactic agent in most dogs.

• Follow the product label dose and frequency of administration directions, and do not concurrently administer multiple products.

However, now that Immiticide is scarce because of technical issues in the manufacturing plant, the AHS has also developed a management plan to help you help heartworm-positive dogs and dogs that haven't completed a full course of adulticidal treatment.

The three primary goals of the management plan are to

· Reduce potential pathology from heartworm infection.

· Maintain the health of a heartworm-positive dog until it can be appropriately treated.

1. Verify the dog's heartworm status with a second antigen test (from a different manufacturer) and perform a microfilariae test in antigen-positive dogs or dogs that have started but not completed adulticidal therapy (because of product unavailability).

2. Pretreat microfilariae-positive dogs with corticosteroids with or without an antihistamine, administer the initial dose of a heartworm preventive (macrocyclic lactone), and clinically observe the dogs for at least eight hours. Treat appropriately should a shock reaction occur.

Adult heartworms will likely still be present in dogs managed with this protocol, but recheck a dog’s heartworm status to reconfirm adult heartworm infection before administering adulticide treatment once Immiticide is again available.